1. Field of the Invention
The invention generally relates to electronics, and in particular, to communications systems.
2. Description of the Related Art
Desirable characteristics of a communications technology are near capacity data rate, flexibility, reliability, robustness to interference, co-existence with other systems, etc. A relatively important characteristic of a communications waveform required to exhibit these characteristics is high dimensionality. For example, a wideband orthogonal frequency division multiplexed (OFDM) system has high dimensionality in frequency. Shannon's theory derives capacity as dimensionality goes to infinity (water filling analogy).
Highly dimensional systems can have more inherent flexibility with regard to how capacity is allocated. Similar benefits are applicable for highly dimensional systems for interference tolerance, coexistence and other desirable properties. An arbitrary application of the concept of dimensionality does not necessarily yield a good waveform. While an OFDM system with a large number of tones can exhibit very good jamming resistance in the presence of narrowband jammers, each tone can be affected by an impulse jammer. It is therefore desirable to incorporate dimensionality on multiple axes: time, frequency, and code space (code space is not independent from the other two in a strict sense but from a functional perspective it is useful to consider separately).